The present invention relates to the production of isocyanate-based foams using hydrocarbons which are vaporizable under foaming conditions as blowing agents. Preferred are those hydrocarbons with boiling points of 10.degree. to 80.degree. at 760 mm Hg, and specified polyether-polyol mixtures in which the hydrocarbon being used as a blowing agent is partly dissolved and partly dispersed, so that an emulsion is formed.
It is well known that isocyanate-based foams can be produced using such hydrocarbons as blowing agents (see, e.g. U.S. Pat. Nos. 3,072,582 and 4,585,807, European Patents 394,769 and 421,269, and German Offenlegeschrift 2,544,560). In closed-cell foamed materials, such blowing agents are efficient as heat insulating cell gases. However, to date, the chlorofluorocarbons (such as trichlorofluoromethane (R 11), dichlorodifluoromethane (R 12) and trichloro-fluoroethane (R 13)) are the insulating and foaming gases most widely used for foamed materials made of polyurethane, polystyrene, polyvinyl chloride, phenol-formaldehyde and the like.
The chlorofluorocarbon blowing agents have the disadvantage that they enter the stratosphere, where they are thought to contribute to the breakdown of the ozone present by reason of their chlorine content. Because of this there are plans to cease the production of chlorofluorocarbons in the near future.
Among the blowing agents which do not have the above disadvantages are hydrocarbons which are vaporizable under foaming conditions, such as n- and iso-pentane and cyclopentane. It has, however, become apparent that not all the requirements of foam technology are met when these hydrocarbon blowing agents are used. In particular, the insulating performance (low thermal conductivity) required for high-quality rigid foam applications is not usually attained.
The object of the present invention was, therefore, to improve the thermal conductivity of rigid polyurethane foams produced with the use of hydrocarbon blowing agents.